Abstract:

The present invention provides a system for window blast protection. The
system includes a first material, which is either elastomeric or
non-elastomeric, which is bonded to a second material, which is
elastomeric when the first material is non-elastomeric, and is
non-elastomeric when the first material is elastomeric. The system also
includes a cover for protecting the materials, where the cover releases
the materials in response to the pressure impact of an explosive blast.
The second material is anchored to the inside of the cover. When the
system is in use, the system further includes a bonding agent for bonding
the first material to a film attached to the inner surface of the window
and an anchoring means for anchoring the outside of the cover to a frame
or wall surrounding the window.

Claims:

1. A system for mitigating the release of window glass fragments by an
explosive blast pressure impact, comprising:a) a first material, having
first and second ends, wherein said first material is either elastomeric
or non-elastomeric;b) a second material, having first and second ends,
wherein said second material is elastomeric when said first material is
non-elastomeric, and wherein said second material is non-elastomeric when
said first material is elastomeric;c) a cover for protecting said first
material and said second material, wherein said cover releases said first
and second materials upon said pressure impact of said explosive
blast,wherein said first material is bonded along its second end to said
first end of said second material, and wherein said second material is
anchored along its second end to an inside of said cover.

2. The system as set forth in claim 1, wherein said first material is
non-elastomeric and said second material is elastomeric.

3. The system as set forth in claim 3, further comprising a third
material, having first and second ends, wherein said third material is
non-elastomeric.

4. The system as set forth in claim 3, wherein said third material is
anchored along its second end to said inside of said cover.

5. The system as set forth in claim 3, wherein said third material
comprises at least one synthetic fabric.

6. The system as set forth in claim 3, wherein said third material
comprises at least one of nylon or rayon.

7. The system as set forth in claim 3, wherein said third material
comprises a mesh.

8. The system as set forth in claim 3, wherein said first, second, and
third materials are folded, rolled, or coiled within said cover.

9. The system as set forth in claim 3, wherein said system has a top
section, a bottom section, and two side sections, wherein said top
section is designed to bind at one edge to a top border of said film,
wherein said bottom section is designed to bind at one edge to a bottom
border of said film, and wherein each of said two side sections is
designed to bind at one edge to a side border of said film, and wherein
another edge of said top, said bottom, and said two side sections is
designed to anchor to said frame or said wall.

10. The system as set forth in claim 9, wherein said top and bottom
sections contain said third material and wherein said side sections
contain said first and second materials.

11. The system as set forth in claim 3, wherein an edge of said first or
second non-elastomeric material is bonded to an edge of said third
material.

12. The system as set forth in claim 3, further comprising a bonding agent
for bonding said third material along its first end to a film attached to
an inner surface of said window.

13. The system as set forth in claim 1, wherein said non-elastomeric
material comprises a synthetic fabric.

14. The system as set forth in claim 1, wherein said non-elastomeric
material comprises nylon or rayon.

15. The system as set forth in claim 1, wherein said elastomeric material
is selected from the group consisting of nitrile, butyl, epichlorohydrin,
hypalon, latex, natural rubber, neoprene, polyurethane, pure gum rubber,
styrene butadiene, santoprene, vinyl, and viton.

16. The system as set forth in claim 1, wherein said elastomeric material
contains slits to reduce the effective thickness of said elastomeric
material.

17. The system as set forth in claim 1, wherein said first material is
glued to said second material, sewn to said second material, or both.

18. The system as set forth in claim 1, further comprising a bonding agent
for bonding said first material along its first end to a film attached to
an inner surface of said window.

19. The system as set forth in claim 1, further comprising an anchoring
means to anchor an outside of said cover to a frame or wall surrounding
said window.

20. The system as set forth in claim 1, wherein said system contains said
window glass fragments resulting from said explosive blast pressure
impact when said blast exerts a pressure of at least about 4 psi.

21. The system as set forth in claim 1, wherein said system contains said
window glass fragments resulting from said explosive blast pressure
impact when said blast exerts a pressure of about 10 psi.

Description:

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001]This application is a continuation-in-part of U.S. patent
application Ser. No. 11/471,806, filed Jun. 20, 2006, which claims
priority from U.S. Provisional Patent Application No. 60/693,024, filed
Jun. 22, 2005, both of which are incorporated herein by reference.

[0003]When a large terrorist bomb is detonated near a building, flying
glass from blown-out windows causes the most injuries. There is a clear
need to harden windows in many government buildings to terrorist blast.
The General Services Administration (GSA) plans to harden 800 existing
government buildings over the next several years. Many new government
buildings will also be glass hardened to blast. Depending on the
perceived threat, GSA requirements are to protect about half the hardened
windows against blasts of 4 psi and the other half against 10 psi.

[0004]Several window-hardening systems have been developed to eliminate or
minimize the threat of injury from glass fragments produced by terrorist
bombs. For new building construction, the typical approach is to use
extra-thick glass (up to one inch) or to use strong ductile polymers such
as Lexan. Retrofitting existing buildings with these approaches is often
prohibitively expensive and, therefore, other approaches are used.

[0005]Current retrofit systems for hardening windows involve adding a film
or curtain on the inside of the window to prevent the glass from flying
into the room. The simplest retrofit system is to cover the inside of the
window with polyester film over the portion of the glass inside the frame
(so-called daylight film). Such films are already frequently used to
limit ultraviolet light transmitted through the window. A blast wave
impinging on glass covered with daylight film will still fracture the
glass but, up to a limit, the film will adhere to the glass fragments.
Furthermore, the film/glass structure raises the blast hardness compared
to a bare window.

[0006]To further increase the blast hardness, the film may be anchored to
the window using a variety of materials. Hardness can also be increased
by a so-called horizontal catch bar mounted at the mid-height of the
window. In this system, the film, with glass fragments still attached, is
arrested by the catch bar as the film folds around it.

[0007]Current systems are insufficient for many applications because they
concentrate the stress at the edge or at the middle of the film, thus
limiting the blast pressure the film can withstand before it fails.
Accordingly, there is a need in the art to develop a window-hardening
method that relieves the stress on the film, has the flexibility to
provide a range of hardness levels up to at least 10 psi, and is simple
and inexpensive to install.

SUMMARY OF THE INVENTION

[0008]The present invention provides a system for window blast protection.
The system includes a first material, having first and second ends, that
is either elastomeric or non-elastomeric. The system also includes a
second material, having first and second ends, that is elastomeric when
the first material is non-elastomeric, and is non-elastomeric when the
first material is elastomeric. The first material is bonded along its
second end to the first end of the second material. Thus, the system
contains two materials that are bonded to one another, a non-elastomeric
material for containing glass fragments generated by the blast and an
elastomeric material for absorbing energy from the blast. The system also
includes a cover for protecting the first and second materials, where the
cover releases the first and second materials in response to the pressure
impact of an explosive blast. The second material is anchored along its
second end to the inside of the cover. When the system is in use, the
system further includes a bonding agent for bonding the first material
along its first end to a film attached to the inner surface of the
window. In addition, the system includes a means for anchoring the
outside of the cover to a frame or wall surrounding the window.

[0009]In a preferred embodiment, the system also includes a third
material, having first and second ends, where the third material is
non-elastomeric. Preferably, the third material is a mesh, and thus
serves to both vent blast pressure and contain glass fragments generated
by the blast pressure impact. Preferably, the third material is anchored
along its second end to the inside of the cover. Also preferably, an edge
of the first or second non-elastomeric material is bonded to an edge of
the third material. When the system is in use, the system further
includes a bonding agent to bond the third material along its first end
to the film attached to the inner surface of the window.

[0010]In a particularly preferred embodiment, the system is divided into a
top section, a bottom section, and two side sections. The top section is
designed to bind at one edge to a top border of the window film, the
bottom section is designed to bind at one edge to a bottom border of the
window film, and each of the side sections are designed to bind at one
edge to a side border of the window film. Another edge of the top,
bottom, and two side sections is designed to be anchored to the frame or
wall surrounding the window. Preferably, the top and bottom sections
contain the third material, and the two side sections contain the first
and second materials. In an alternative embodiment, the placement of the
panels can be rotated 90° such that the panels described above as
being at the top and bottom are now at the sides and the panels
identified as the sides are now positioned at the top and bottom of the
window restraint system.

BRIEF DESCRIPTION OF THE FIGURES

[0011]The present invention together with its objectives and advantages
will be understood by reading the following description in conjunction
with the drawings, in which:

[0012]FIG. 1 shows an embodiment of a system according to the present
invention.

[0013]FIG. 2 shows a mechanism of action of a system according to the
present invention.

[0014]FIG. 3 shows another embodiment of a system according to the present
invention.

[0015]FIG. 4 shows an example of a material layout for a system according
to the present invention.

[0016]FIG. 5 shows an example of sections of a system according to the
present invention.

[0017]FIG. 6 shows examples of a means of anchoring a system according to
the present invention to a wall or frame (A) and a means of binding a
system according to the present invention to a window film.

[0018]FIG. 7 shows blast pressure data from a test of a blast-resistant
window system according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0019]FIG. 1A shows an example of a blast-resistant window system 100
according to the present invention. The system 100 includes a first
material 110, with first end 112 and second end 114, and a second
material 120, with first end 122 and second end 124. First material 110
is either elastomeric or non-elastomeric. Second material 120 is
elastomeric when first material 110 is non-elastomeric, and is
non-elastomeric when first material 110 is elastomeric. In a preferred
embodiment, first material 110 is non-elastomeric, and second material
120 is elastomeric. First material 110 is bonded at second end 114 to
first end 122 of second material 120. Second material 120 is anchored at
its second end 124 to the inside of cover 140 through anchoring means
130. The anchoring means may a bonding agent, screw-like fasteners with
or without reinforcing means, or a combination thereof. If anchoring
means 130 is a bonding agent, it may be any bonding agent known in the
art, including but not limited to glue and Velcro. First material 110 may
be bonded to second material 120 using any method known in the art,
including but not limited to sewing, gluing, or gluing and sewing.
Preferably materials 110 and 120 are folded, rolled, or coiled within
cover 140 for compactness.

[0020]The non-elastomeric material may be any non-elastomeric material
known in the art, including but not limited to a synthetic fiber, such as
rayon or nylon. Similarly, the elastomeric material may be any
elastomeric material known in the art, including but not limited to
nitrile, butyl, epichlorohydrin, hypalon, latex, natural rubber,
neoprene, polyurethane, pure gum rubber, styrene butadiene, santoprene,
vinyl or viton. The elastomeric material preferably contains slits to
reduce the effective thickness of the material.

[0021]FIG. 1B shows an example of how blast-resistant window system 100
would be fit to a window and a frame or wall surrounding the window. FIG.
1B shows a side view of window 180, anchored in wall 160, and covered on
the inside with protective film 170. (Only a small section of window 180
is shown, for clarity). The first end 112 of material 110 is bonded with
bonding agent 190 to film 170. Any bonding agent known in the art may be
used as bonding agent 190. In a preferred embodiment, first end 112 is
bonded to a metal or plastic transition strip (not shown), and this
transition strip is in turn bonded to film 170. In another preferred
embodiment, a layer of Spectra felt and/or fabric (not shown) may be used
in between first end 112 and film 170. This layer serves to reduce the
stress concentration at the edge of the glass window 180. In a
particularly preferred embodiment, this layer includes a layer of Spectra
felt over a layer of strong Aramid woven fiber. This combination has been
shown by others to greatly enhance protection against the fragments from
a failed turbine engine by reducing the local stress concentrations from
the edges of the fragments. If glass fragments cause materials 110 and
120 to fail at other locations away from the edge of the glass, the
Spectra felt layer may be extended and enclosed with materials 110 and
120 inside cover 140.

[0022]Cover 140 is anchored to frame or wall 160 via anchoring means 150.
Anchoring means 150 may be any anchoring means known in the art,
including but not limited to various adhesives or a vulcanizing bonding
process. The cover is preferably semi-rigid to permit the deployment of
the blast-restraint system.

[0023]Blast-resistant window system 100 is designed to respond to an
explosive blast pressure impact as shown in FIG. 2. FIG. 2A shows a side
view of system 100, which is bonded to film 170, which is in turn
attached to the inner surface 182 of window 180. System 100 is also
anchored to wall or frame 160. In FIG. 2B-D, pressure from an explosive
blast hits the outside 184 of window 180. Sufficient blast loading will
produce failure of the glass in window, such that it fragments into
pieces 186. The film 170 and glass fragments 186 then translate, uncoil
materials 110 and 120, and gradually stretch the elastomeric material
until the elastomeric material arrests the glass and film (FIGS. 2C and
D). The folds 210 in materials 110 and 120 may be lightly bonded to
themselves so that they unfold as shown in FIG. 2.

[0024]This system has several advantages over those that use solely an
elastomeric material or a non-elastomeric material. For a system using
all non-elastomeric material, when the material reaches the limit of
deployment, it must absorb any remaining blast pressure and bring the
glass velocity down to zero fps. Thus, the material must be of sufficient
strength such that when fully extended, it will bring the glass velocity
down to zero fps. If only elastomeric material is used, the material
necessary to bring the glass velocity to zero fps will be several times
thicker than a version using only non-elastomeric material, which adds
considerably more bulk to the restraint system and requires a much larger
and obstructrive/obtrusive storage container around the window. In
contrast, if both a non-elastomeric material and an elastomeric material
are used, as in the inventive system, the strength requirement of the
non-elastomeric material can be reduced, and the amount, and thus the
total bulk, of the elastomeric material can be reduced. This allows the
inventive system to bring the glass velocity down to zero fps and achieve
the same degree of containment of the glass window fragments as single
material systems, but with a significant reduction in size of the overall
system. Preferably, the system according to the present invention
contains window glass fragments resulting from an impact of an explosive
blast pressure of at least about 4 psi, more preferably about 10 psi.

[0025]FIG. 3 shows a frontal view of a preferred embodiment of a deployed
blast-resistant window system 300 according to the present invention.
System 300 includes two sides, a top, and a bottom (only one side 320 and
a top 330 are shown for clarity). Each side contains a first material
110, with first end 112 and second end 114, and a second material 120,
with first end 122 and second end 124. First material 110 is either
elastomeric or non-elastomeric. Second material 120 is elastomeric when
first material 110 is non-elastomeric, and is non-elastomeric when first
material 110 is elastomeric. First material 110 is bonded through a
bonding agent (not shown) at first end 112 to window film 170, which is
attached to window fragments 186. First material 110 is bonded at second
end 114 to first end 122 of second material 120. Second material 120 is
anchored at its second end 124 to the inside of cover 140. The top and
bottom of system 300 are made of third material 310, with first end 312
and second end 314. Third material 310 is anchored along its second end
314 to the inside of cover 140. Third material 310 is bonded with a
bonding agent (not shown) along its first end 312 to film 170. In
addition, cover 140 is anchored to wall or frame 160.

[0026]Preferably, third material 310 is non-elastomeric, and is made of at
least one synthetic fabric, such as rayon or nylon. Third material 310
may be identical to, different to, or partially made of first or second
non-elastomeric material. Preferably, all or part of third material 310
is a mesh, as indicated by the crossed lines in FIG. 3. Similar to first
and second materials 110 and 120, third material 310 is preferably
folded, rolled, or coiled within cover 140 prior to deployment.

[0027]FIG. 4 shows a preferred plan for assembling materials 110, 120, and
310 into a system according to the present invention. In this plan, 420
and 440 indicate side panels, 430 indicates a bottom panel, and 450
indicates a top panel. Side panels 420 and 440 are each made of first
material 110, having first end 112 and second end 114, and second
material 120, having first end 122 and second end 124. First material 110
is bonded 460 along its second end 114 to the first end 122 of second
material 120. In addition, side panel 420 is bonded 410 to bottom panel
430, which is in turn bonded 410 to side panel 440, which is in turn
bonded to top panel 450. Preferably, top panel 450 is also bonded 412 to
side panel 420, forming a tunnel-like structure. Also preferably, it is
the non-elastomeric material in side panels 420 and 440 that is bonded to
top and bottom panels 430 and 450. While 110 is shown to be the
non-elastomeric material in this figure, 120 could in fact be the
non-elastomeric material. All materials may be bound using any method
known in the art, including but not limited to sewing, gluing, or sewing
and gluing. In an alternative embodiment, 420 and 440 are top and bottom
panels, respectively, and 430 and 450 indicate side panels

[0028]FIG. 5 shows an embodiment of the present invention in which the
system has a top section 510, bottom section 520, (FIG. 5A) and two side
sections 530 (FIG. 5B). The top section 510 is designed to bind at an
edge 512 to a top border 172 of film 170, and at an edge 514 to a frame
or wall 160 surrounding window 180. Bottom section 520 is designed to
bind at an edge 522 to a bottom border 174 of film 170, and at an edge
524 to a frame or wall 160 surrounding window 180. Side sections 530 are
designed to bind at an edge 532 to a side border 176 of film 170, and at
an edge 534 to a frame or wall 160 surrounding window 180.

[0029]Also preferably, side sections 530 contain a cover and the first and
second materials. In an alternative embodiment, top section 510 and
bottom section 520 contain the first and second materials, and side
sections 530 contain the third material.

[0030]FIG. 6A shows an example of how a system according to the present
invention could be anchored to a frame or wall surrounding a window. This
example is illustrative only. Any anchoring means known in the art could
be used to anchor the system to the frame or wall. FIG. 6A shows frame or
wall 160 with indentation 610. Cover 140 is bonded on both sides by
double-stick tape 620 and 622. Double-stick tape 622 is in turn bonded to
reinforcing strip 630. Reinforcing strip 630 may be, e.g., plastic,
aluminum, etc. Reinforcing strip 630 and material 650 are bonded with
adhesive 640. In this case, material 650 would be either the second or
third material. Material 650 is in turn bonded to a reinforcing strip 660
with counter-sink hole 662 to receive fastener 670. Fastener 670 may be a
screw, bolt, etc., and goes through double stick tape 620 and 622, cover
140, reinforcing strip 630, adhesive 640, and material 650 where
indicated by the dashed lines.

[0031]FIG. 6B shows an example of how a system according to the present
invention is bonded to a window film. This example is illustrative only.
Any bonding agent known in the art could be used to bond the system to
the window film. FIG. 6B shows frame 160, holding window 180. Film 170 is
attached to window 180 using any method known in the art. Material 690 is
bonded to film 170 with adhesive backed Velcro 680. Material 690 is in
this case the first or third material. Velcro 680 is preferably of the
hook and loop sort.

EXAMPLES

[0032]1. We have performed a dynamic one-dimensional analysis of this
approach, in which we represented the window and the first and second
materials with a simple spring-mass system. The analysis shows that we
can design window hardness to survive a wide range of blast loading. In
particular, we can design a practical system for a 3-foot-wide by
4-foot-high 1/4-inch-thick window that meets both levels of GSA hardness
requirements (i.e. 4 psi and 10 psi). These two systems both use
elastomeric material that has a maximum stress of 800 psi and maximum
strain of 450%. In one example of a system designed to withstand 10 psi
blast pressure, the elastomeric material was neoprene at 0.030 inch thick
and 18 inches long (i.e., in the direction of deployment) with slits in
the central 12 inches aligned in the direction of deployment. Hardness
levels above 10 psi may also be obtained by adjusting the size of the
elastomeric material size or by choosing a different type of elastomeric
material.

[0033]2. An important feature of this invention is the attachment of the
first material to the window film. In a preferred embodiment, we bonded
both the film and the first material to a metal or plastic transition
strip. To check the attachment strength, we performed static pull tests
on an aluminum strip that had neoprene rubber bonded to one end and
window film bonded to the other. For a two-inch overlap between the
aluminum and the film, we performed a simple static test with no damage
to the test specimen at 50 lb per inch; the actual strength appears to be
much higher. The 10-psi design requires a bond strength of only 72 lb per
inch.

[0034]3. To test the blast hardness of a window with a hybrid
elastomeric/non-elastomeric containment system as described above, test
windows were mounted in a rigid wall one foot from the end of an
8-ft-diameter, 257-ft-long explosively driven shock tube. The desired
load is a peak pressure of at least 10 psi and an impulse of at least 89
psi-msec. We designed an explosive charge that would produce the desired
load on the wall. The charge was made of 525 gms of C-4 explosive and is
suspended on the axis of the tube 142 feet from the wall. A high speed
video camera was positioned behind the wall and aimed at right angles to
the axis of the tube. The performance of the window system was evaluated
by the observations in the video record and by observing where the glass
fragments ended up after the test. Pressure transducers were mounted
adjacent to the test window to record the amplitude and duration of the
test blast pressure wave at the surface of the window.

[0035]FIG. 7 represents blast pressure data from a test of a
blast-hardened window. The actual peak pressure (indicated by a black
line) of the blast at the surface of the window was about 9 psi when 525
grams of high explosive were used. The hybrid elastomeric/non-elastomeric
system successfully contained glass fragments of the window at this blast
pressure and duration. These data were extrapolated to the expected blast
pressure forces if 575 grams of the same explosive were used. The
extrapolated date resulted in a blast pressure of over 13 psi (grey
line). The curves indicated by arrow 710 are the pressure data, and the
curves indicated by arrow 720 are the impulse data. The hybrid
elastomeric/non-elastomeric system successfully contained glass fragments
of the window at this blast pressure and duration.

[0036]As one of ordinary skill in the art will appreciate, various
changes, substitutions, and alterations could be made or otherwise
implemented without departing from the principles of the present
invention. For example, while the invention has been described with first
and second materials on the sides, and third material on the top and
bottom, the reverse could be true. Accordingly, the scope of the
invention should be determined by the following claims and their legal
equivalents.